So-called field devices are often applied in industrial plants for control and/or monitoring of a process running in the plant. The energy supply of these field devices occurs, in such case, for example, via an electrical current loop, to which a field device or a number of field devices are connected. The supply of one or more field devices with electrical energy occurs, in such case, via a feeding device, such as, for example, a power supply, which provides the energy required for operation of the field device, respectively field devices. The energy is provided, for example, in the form of a DC voltage.
Especially in the case of start-up and the therewith connected start procedure of one or more field devices, the field devices exhibit an increased voltage- and/or electrical current requirement. This is caused, for example, by the charging of capacitors present in the field device. An apparatus for start-up of field devices is known, for example, from (laid open international application) Offenlegungsschrift WO 2012000996. By means of a start-up circuit proposed there, the field devices are supplied successively with a voltage provided by a voltage source.
It is known for the energy supply of field devices to use so-called measurement transmitter power supply devices. Such measurement transmitter power supply devices utilize, for example, a grid connection, from which electrical energy is removed and supplied to the field devices. Especially, power supplies are known, which fulfill requirements or explosion protection and have a power-limited release of electrical energy.
This power limiting conflicts, however, with the energy requirement especially during start-up of one or more field devices. For example, field devices have during start-up an increased power requirement. This is caused, for example, such as already mentioned, by the initial charging of capacitors present in the field device. Furthermore, it is required in the case of the start-up initially to load data, for example, into a working memory of the field device, or to execute certain initializing- and self-calibration functions.
It is, thus, in given cases, not possible to start-up a field device, which is connected to a measurement transmitter supply device that is power-limited according to the ignition protection type, intrinsic safety, since the power issued from the feeding device is insufficient for starting the field device.